Do filters have a right way round?

[CraigT82]

I'm using a IR cut filter for planetary imaging and I have it screwed into the back of the nosepiece of my ASI185 camera (the thread continues all the way from the front to the back)... I do this because when I had it screwed in the normal place at the front, I got some strong internal reflections due to it being very close to the barlow element that I also have screwed into the front.

 

In this position at the back the filter is facing the opposite way to what it would fitted at the front, does this cause an issue?  I know some DSO imaging filters are marked so they're fitted the right way round but would it be the same on an IR cut filter??  Or my 850nm IR pass filter for that matter?

 

Many thanks!

Craig

[Adam J]

Absorption or reflective filers are usually bi-directional but interference based filters are not. An IR filter may be absorption based so i would guess yes. You normally have a little chevron on the rim of directional filters indicating the correct direction.

[CraigT82]

Thanks for that, the GSO filter is stated as being dichroic (interference) so I guess I better start using it the right way round